Many photographers use digital cameras to capture images. Unlike conventional wet processing of silver halide film and papers, digital images can be printed directly onto sheets of paper. Color images may be printed using ink jet printers, multicolor transferable toner printers, heat sensitive coated paper printers, or thermal dye transfer printers. Many mass-market retail establishments have user-friendly kiosks where shoppers may make color prints. A large number of these kiosks use thermal dye transfer printers. Because the kiosks use large amounts of paper, the images may be printed on a continuous web of paper. The images are later separated from each other and from the web by a suitable cutter or knife. Such prints have dye images that bleed to the edges in the latitudinal and longitudinal directions. These prints are known as borderless prints and are the most popular prints with consumers.
Thermal dye transfer printers generate very high quality images. As such, a number of photographers want their own thermal dye transfer printer. However, it is impractical and not cost effective to supply continuous web paper for the images. It would also be expensive to supply built-in paper cutters and knives to provide borderless prints. To meet the demand for borderless prints, there are known methods of bleeding the latitudinal edges so that there is no border on the tops and bottoms of prints. See, for example, U.S. Pat. Nos. 5,441,353; 5,196,863; and 5,499,880. However, those techniques cannot provide prints that bleed to the longitudinal borders.
To solve this problem and provide full borderless prints, others use special manufactured sheets of paper that carry perforated longitudinal leading and trailing borders. The leading edge and the trailing edge of the paper are perforated to let the user remove them from the finished print. In this way, the printed image may slightly exceed the area between the perforations. The excess portion of the image is removed with the perforated leading and trailing edge to provide the user with a borderless image.
A key drawback of the existing solution is the requirement for special paper with perforations on the leading and trailing edges. Such paper is expensive to manufacture and has little or no other market outside of printing digital images. In addition customers are dissatisfied with the requirement for tearing off the perforated edges of the printed images. However, conventional printers are not configured to use ordinary paper and provide borderless prints.
In a conventional thermal printer, paper is clamped between a capstan roller and a pinch roller and pulled through a nip between a thermal print head and the platen. The capstan and pinch rollers are driven by a stepper motor that provides both precise movement and control of the paper sheet. The print head and platen capture a web of donor material with dye and press it against the paper. The platen spins freely while the web and receiver are pulled past the print head. Heat from the thermal head transfers dye from the donor web onto the receiver paper to create an image.
An example of a prior art thermal dye transfer printer 600 that provides monotone, multi-tone or full color printing is shown in FIG. 6. A printer 600 has a sheet 8 that is driven along a print path 4 by a set of tension rollers 30, 31. The print head 25 is opposite a free spinning platen 33. Donor and supply rollers 20, 22 support a web 21 of thermal dye donor material. A bias spring 36 presses the print head 25 against the donor web 21 that contacts the receiver paper. A pinch spring 35 urges pinch roller 30 against capstan roller 31 that is turned by a stepper motor 34. A transmission, such as a belt 32, connects the capstan roller 31 to stepper motor 34. The leading edge of sheet 8 is fed into a pinch or nip between rollers 30, 31. They pull the sheet and the web past print head 25 where donor material is transferred to the sheet 8. The printer 600 uses paper with a perforated leading and trailing edges. Dye is transferred to the receiver paper and slightly beyond the perforations. When the perforated edges are removed, the longitudinal ends the print are without any border, and the print appears to bleed to the ends of the sheet.